Sansui VX-99 Modification


I found a Sansui VX-99 (NTSC) video mixer a while back. It didn’t seem to be fully working when I got it. Which is fine, it was in an as-is pile. I was just hoping to be able to use it to add some extra static and noise to live footage for visuals if nothing else. After opening it up to give a fader some more support using some hot glue, I still couldn’t get both channels of video to display at the same time. I eventually figured out that in order to mix the two video sources, you have to press the gen-lock mix button. After doing this, the mixer mostly works. I still have yet to figure out how to get the thing to display any changes when you press on the RGB color buttons. I’m assuming that these allow you to fade to a color instead of black, which I wouldn’t usually want, but could be interesting if you were doing some sort of video feedback.

Old video equipment is very frustrating. It causes all sorts of video glitches (can be good), which breaks the sync (bad) and causes your nice image to be indecipherable or, worse yet, blue screen. I wish the default was black.

I’m having fun playing with this thing. It has tons of adjustments inside using little trimmer dials. The VX-99 is a very capable video device when you include the possibilities of all of these dials, although since it is very hard to get back to a normal image I can understand why they left these out of reach. I am going to find some dials that I can mount on the outside of the case to replace the ones inside. I don’t like to destroy old things, but this one is much more valuable if I can use all of these settings without having the case lying open. I’ll make sure I put on markers for a “normal” setting once I figure them out again.

You need to undo the silver screw in order to get the case off. It’s the ground connection between the bottom and top of the case. The power switch also held the case on, so you have to lift the case by the power button until it comes off.

Since a large number of the tiny trimmer potentiometers inside of this video mixer do interesting things that don’t exist in the original controls, I want to add controls to the outside of the case. The hardest thing about this is finding potentiometers with similar values to the ones originally in the mixer as well as hopefully looking somewhat natural on a very 80s looking device.

The varieties of dials and their markings are:
(most likely only helpful for myself)

103, 222, 223, 224, 471, 472, 473

blue (smaller)
721C 471, 721C 472, 612d 333, 5398 683, 722C 104, 609d 223
650A 332, 710C 222, 706C 103

silver tall box with dial inside
1x – 4835 0000 760
2x – 4835 0100 760

blackandyellowdial short black box with yellow top
No markings



2 thoughts on “Sansui VX-99 Modification

  1. Polyphasicmusic

    Hi. I just acquired one of these video mixers and am wondering if you had any further luck with is thing? I am trying to figure out what do with it.

    1. Ian Page-Echols

      I still use it to process some video but I didn’t end up modifying it much. Adding dials to a flat and angular piece of 80s gear seemed a bit weird. I should probably start putting in connectors for external controls on some of my equipment so that I don’t even have to worry about that. It would also be fairly hard to get the original hidden controls out without ruining the mixer. And since I like what it does in stock form, I’d like to avoid that. Maybe I should find a 2nd one?

      Let me know if you end up figuring out anything interesting or even just linking to some video if you do something fun with it in stock form.


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